Abstract
The instability and collapse of the extraction borehole seriously affects the gas extraction effect, and it is of great significance to study the efficient borehole protection technology to improve the stability of the borehole and ensure the gas extraction effect. The purpose of this study is to develop an environmentally friendly borehole protection material with high strength, high permeability and controllable setting time, and then propose a borehole synergistic protection technology for in-hole screen protection and grouting reinforcement. The foaming agent mother liquor was obtained by hydrolysis of human slag, the composite protein foaming agent was prepared by improving the compounding of the mother liquor, pulverized coal was used instead of fly ash as mineral admixture, the water-cement ratio, material ratio and foaming agent addition amount of the optimal grouting material were determined by orthogonal tests, and the foam concrete with high strength and high permeability was prepared, and its on-site construction feasibility was verified by the dynamic curing characteristics experiment of coagulation time and fluidity. Finally, the borehole synergistic protection technology of in-hole screen protection and grouting reinforcement was proposed, and industrial tests were carried out in the field. The results showed that: (1) Sodium hydroxide hydrolyzed human hair residue was used as a composite protein foaming agent mother liquor material, and the optimal foam performance was determined to be 2 g/L sodium laureth sulfate (SLS) + 0.3% calcium stearate through the compound improvement experiment. (2) Pulverized coal replaces the commonly used material fly ash as concrete admixture, which can effectively use waste resources, improve the strength and durability of concrete, and reduce carbon emissions and environmental pollution. (3) The prepared hole protection material has high permeability and compressive strength, when the water-cement ratio is 0.7:1, the foam content is 25 ml, the pulverized coal is 30 g, the silica fume is 5 g, and the polypropylene is 0.2 g, the compressive strength of the material is 13.665 MPa, the permeability is 2.12MD, the porosity is 22.019%, and the coagulation time is 401 min to 418 min, which meets the requirements of initial solidification within 1-3 days. The fluidity is 320 mm, which is in line with the field experiment. (4) The proposed screen pipe and grouting borehole collaborative protection technology can realize the internal and external coordinated protection of the borehole, the grouting outer layer protection can be poured and solidified according to the shape of the borehole and the falling coal and rock, the inner layer protection of the screen pipe can enhance the stability of the borehole and the grouting material after solidification, effectively prevent the instability and collapse of the borehole wall, ensure the smooth borehole extraction channel, and effectively improve the gas extraction efficiency.